On my Mediawiki 1.28 installation, I encounter these errors 'Cannot flush snapshot because writes are pending' with several extensions (EmailToWiki, HTML2Wiki, DataTransfer)

Here some excerpts from the log-file:

exception] [e258cf43474ed3ddbbb499ac] /Special:ImportCSV DBUnexpectedError from line 2852 of /var/www/html/mediawiki/includes/libs/rdbms/database/Database.php: MWCallableUpdate::doUpdate: Cannot flush snapshot because writes are pending (WikiPage::insertOn, Revision::insertOn, Revision::insertOn, WikiPage::updateRevisionOn, WikiPage::updateRedirectOn, RecentChange::notifyNew).

[Bug56269] Exception thrown with an uncommited database transaction: [e258cf43474ed3ddbbb499ac] /Special:ImportCSV DBExpectedError from line 1096 of /var/www/html/mediawiki/includes/libs/rdbms/loadbalancer/LoadBalancer.php: MWCallableUpdate::doUpdate: Flush failed on server(s) localhost: MWCallableUpdate::doUpdate: Cannot flush snapshot because writes are pending (WikiPage::insertOn, Revision::insertOn, Revision::insertOn, WikiPage::updateRevisionOn, WikiPage::updateRedirectOn, RecentChange::notifyNew).

[Bug56269] Exception thrown with an uncommited database transaction: [e258cf43474ed3ddbbb499ac] /Special:ImportCSV DBUnexpectedError from line 2657 of /var/www/html/mediawiki/includes/libs/rdbms/database/Database.php: Invalid atomic section ended (got WikiPage::doCreate).

salty, with a "bite" from its blue veining requestId=e258cf43474ed3ddbbb499ac (id=337,timestamp=20170227085845) t=243 error=DBUnexpectedError: Invalid atomic section ended (got WikiPage::doCreate).

Start request GET /index.php?action=emailtowiki&prefix=EmailToWiki

[exception] [e258cf43474ed3ddbbb499ac] /index.php?action=emailtowiki&prefix=EmailToWiki DBUnexpectedError from line 2852 of /var/www/html/mediawiki/includes/libs/rdbms/database/Database.php: MWCallableUpdate::doUpdate: Cannot flush snapshot because writes are pending (WikiPage::insertOn, Revision::insertOn, Revision::insertOn, WikiPage::updateRevisionOn, WikiPage::updateRedirectOn, RecentChange::notifyNew).

Bug56269] Exception thrown with an uncommited database transaction: [e258cf43474ed3ddbbb499ac] /index.php?action=emailtowiki&prefix=EmailToWiki DBExpectedError from line 1096 of /var/www/html/mediawiki/includes/libs/rdbms/loadbalancer/LoadBalancer.php: MWCallableUpdate::doUpdate: Flush failed on server(s) localhost: MWCallableUpdate::doUpdate: Cannot flush snapshot because writes are pending (WikiPage::insertOn, Revision::insertOn, Revision::insertOn, WikiPage::updateRevisionOn, WikiPage::updateRedirectOn, RecentChange::notifyNew).

[Bug56269] Exception thrown with an uncommited database transaction: [e258cf43474ed3ddbbb499ac] /index.php?action=emailtowiki&prefix=EmailToWiki DBUnexpectedError from line 2657 of /var/www/html/mediawiki/includes/libs/rdbms/database/Database.php: Invalid atomic section ended (got WikiPage::doCreate).

Maybe something is wrong with my installation, so any help is highly welcome!